A Cosmic Necklace Larger than a Solar System
The "Necklace Nebula," also called PN G054.2-03.4, is the exploded
aftermath of a giant star that came too close to its Sun-like binary
companion. The two stars that produced the Necklace Nebula live in a
relatively small orbit about each other. They have a period of 1.2
days and a separation on the order of 5 times the radius of the Sun.
Evidence for the existence of the two-body system arises from the
nebula's appearance of a half-light-year-wide equatorial ring of dense
material near the inner portion of the nebula. The expanding elliptical
ring is composed of bright, dense knots of glowing hydrogen and oxygen
gas. Each knot also dons a small tail pointing away from the central star.
The clumpy appearance of the ring may have been caused by density
fluctuations in the shared material of the binary stars prior to the
explosion, or possibly by magnetic field lines present in the giant star as
it began to expand and shed off its outer layers.
A fast, collimated outflow of nitrogen gas from the binary system has
formed faint lobes and polar caps extending in the direction
perpendicular to the ring. Edge to edge, the nebula is nearly 9 light-years
long, over twice the distance between our Sun and our nearest stellar
companion, Proxima Centauri.
Astronomers studying PN G054.2-03.4 predict that the outer lobes of gas
were ejected about 10,000 years ago, before the two stars began sharing
material. The inner ring of material was created only about 5,000 years
ago (and relatively recent on astronomical timescales), and shares the
same plane as the orbit of the two stars.
The Necklace Nebula is located about 15,000 light-years away in the
northern constellation Sagitta. It was recently discovered in 2005 from IPHAS, the INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane.
The Wide Field Camera 3 (WFC3) detector onboard Hubble was used to
observe the Necklace Nebula on July 2, 2011. Hubble's WFC3 broadband
filters, which show the colors of the galactic field stars, were used along
with narrowband filters that show emission from the gases that make up
the planetary nebula. In this composite image, ionized hydrogen gas is
shown in blue, oxygen gas in green, and nitrogen gas in red. The field
stars appear mainly white, with a reddish tint, which is indicative of the
older population stars that make up the disk of our Milky Way galaxy.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)